1. Field of the Invention
The present invention relates to a built-in-electronic-component substrate, which includes a core substrate, an electronic component mounted on one main surface of the core substrate and a resin layer provided such that the electronic component is embedded therein, and relates to a manufacturing method for the built-in-electronic-component substrate.
2. Description of the Related Art
In recent years, with continuing reduction in the thickness of mobile electronic appliances, built-in-electronic-component substrates, which have a reduced substrate thickness due to electronic components being embedded inside the substrates, have been proposed, as seen in International Publication No. 2011/135926, for example.
FIG. 17 is a sectional view of a built-in-electronic-component substrate 100 described in International Publication No. 2011/135926. In the built-in-electronic-component substrate 100 illustrated in FIG. 17, electronic components 101 and 102 are mounted on a core substrate 108 and a resin layer 109 is formed such that the electronic components 101 and 102 are embedded thereinside.
The built-in-electronic-component substrate 100 is lightweight and has an advantage in that there are few restrictions on the electronic components that may be built thereinto since it is not subjected to high-temperature firing as with ceramic substrates.
Here, multilayer ceramic capacitors are considered as the electronic components 101 and 102 embedded in the resin layer 109 of the built-in-electronic-component substrate 100 described in International Publication No. 2011/135926. FIG. 18 illustrates a sectional view of a multilayer ceramic capacitor 201.
The multilayer ceramic capacitor 201 includes a ceramic multilayer body 202 and a first outer electrode 203 and a second outer electrode 204 provided on a surface of the ceramic multilayer body 202. The ceramic multilayer body 202 is formed by stacking and connecting in parallel or substantially parallel with each other capacitor elements in each of which a ceramic dielectric layer 205 is interposed between a first inner electrode 206 and a second inner electrode 207. Such a multilayer ceramic capacitor 201 is excellent in terms of reliability and durability and can realize a large capacitance despite being small in size.
A high-dielectric-constant ceramic material having barium titanate as a base material is often used as the material of the ceramic dielectric layers 205 of the ceramic multilayer body 202 in the small-size large-capacitance multilayer ceramic capacitor 201. When a voltage is applied to the multilayer ceramic capacitor 201 including the ceramic multilayer body 202, a strain is generated in the ceramic multilayer body 202 in accordance with the size of the applied voltage due to the electrostrictive effect and the inverse piezoelectric effect. As a result, the ceramic multilayer body 202 repeatedly undergoes expansion in a stacking direction of the ceramic multilayer body 202 and contraction in a planar direction perpendicular or substantially perpendicular to the stacking direction.
In recent years, with the progress made in reducing the size and thickness of the multilayer ceramic capacitor 201, the intensity of the electric fields applied to the dielectric layers has increased and therefore the size of the strain acting in the ceramic multilayer body 202 has also increased.
Here, a case in which the multilayer ceramic capacitor 201 is mounted on a substrate B using joining members S such as solder as illustrated in FIG. 19A will be considered. When a voltage is applied to the multilayer ceramic capacitor 201, as illustrated in FIG. 19B, a strain generated in the ceramic multilayer body 202 causes the substrate B, which is fixed to the multilayer ceramic capacitor 201 by the joining members S, to vibrate.
If an acceleration sensor such as a shock sensor were mounted on the substrate B, it is possible that this vibration of the substrate B would cause erroneous operation of the acceleration sensor.
In addition, if the frequency of this vibration is within the range of 20 Hz to 20 kHz, which the frequency range of audible sound, the vibration would be perceived by the human ear as an audible sound. This phenomenon is called acoustic noise and is an issue in making electronic appliances quiet and in the design of power supply circuits of various applications such as laptop computers, cellular phones and digital cameras.
When the multilayer ceramic capacitor 201 is mounted on the substrate B using the joining members S as described above and is further embedded in a resin layer as described in International Publication No. 2011/135926, it is thought that the strain generated in the ceramic multilayer body 202 will be transmitted to the substrate B and to the joining members S and the resin layer. In such a case, there is a fear that the above-described vibration of the substrate B will become larger and that the audible sound will become louder.